Part 3 – Membrane Potentials, Ion Channels, and Resting Membrane Potential

What is voltage in the context of the nervous system?

The measure of potential energy generated by separated electrical charges across a membrane.

What is current?

The flow of electrical charge (ions) between two points.

What is resistance?

The hindrance to charge flow provided by the plasma membrane.

What is an insulator?

A substance with high electrical resistance that prevents charge flow.

What is a conductor?

A substance with low electrical resistance that allows charge flow.

How do neurons use electrical signals?

They use changes in membrane potential to receive, integrate, and send information.

What is the resting membrane potential (RMP)?

The difference in electrical charge across the plasma membrane of a resting neuron (approximately –70 mV).

Why is the inside of the neuron negatively charged relative to the outside?

Because there are more negatively charged proteins and fewer positive ions inside compared to the extracellular fluid.

What causes the resting membrane potential?

The unequal distribution of sodium (Na⁺) and potassium (K⁺) ions and the selective permeability of the plasma membrane.

Which ion has the greatest influence on resting membrane potential?

Potassium (K⁺) because the membrane is more permeable to K⁺ than to Na⁺.

What happens when potassium ions (K⁺) move out of the cell?

The inside becomes more negative, establishing an electrical gradient that opposes further K⁺ movement.

What is the role of sodium ions (Na⁺) in resting potential?

Na⁺ tends to diffuse into the cell, but the membrane’s low permeability to Na⁺ limits this movement.

What is the role of the sodium-potassium pump (Na⁺/K⁺-ATPase)?

It actively transports 3 Na⁺ ions out and 2 K⁺ ions in, maintaining the concentration gradients and resting potential.

How does the Na⁺/K⁺ pump contribute to the resting potential?

It offsets passive ion leaks and maintains ionic balance, requiring ATP for continuous operation.

What are ion channels?

Membrane proteins that allow the selective movement of ions across the plasma membrane.

What are leakage (non-gated) channels?

Channels that are always open and allow ions to move along their electrochemical gradients.

What are gated channels?

Channels that open or close in response to specific stimuli.

What are chemically (ligand)-gated channels?

Channels that open when a neurotransmitter or chemical binds to a receptor.

What are voltage-gated channels?

Channels that open or close in response to changes in membrane potential.

What are mechanically gated channels?

Channels that open or close in response to physical deformation of the receptor (such as touch or pressure).

How do ions move through channels?

Along both chemical concentration and electrical gradients — together called the electrochemical gradient.

What are changes in membrane potential used for?

Communication, signaling, and control of muscle contraction and gland activity.

What causes changes in membrane potential?

Alterations in ion concentrations or membrane permeability to specific ions.

What are depolarization and hyperpolarization?

Depolarization: inside becomes less negative (closer to zero); Hyperpolarization: inside becomes more negative than the resting potential.

What is repolarization?

The return of the membrane potential back toward resting levels after depolarization.

What are graded potentials?

Short-lived, localized changes in membrane potential that decrease in magnitude with distance.

How are graded potentials triggered?

By a stimulus that opens chemically gated ion channels.

Where do graded potentials occur?

Typically on dendrites and the cell body (soma).

What determines the strength of a graded potential?

The amount of stimulus and the number of open ion channels.

How do graded potentials travel?

They spread passively but decay quickly with distance due to current leakage.

Can graded potentials trigger action potentials?

Yes, if the graded potential is strong enough to reach threshold at the axon hillock.

What is the main difference between graded and action potentials?

Graded potentials are short and decremental, while action potentials are long-distance and non-decremental.

What is the resting potential value of most neurons?

Approximately –70 millivolts (mV).

What would happen if the sodium-potassium pump stopped working?

The ionic gradients would dissipate, the resting potential would vanish, and neuronal signaling would fail.

What is the overall importance of membrane potential?

It provides the basis for electrical signaling and communication in the nervous system.